Cellular wireless is an increasingly popular means of personal communication in the modern world. People are using cellular wireless networks for the exchange of voice and data over wireless devices, such as cellular telephones, personal digital assistants (“PDAs”), cellular telephone modems and other devices. In principle, a user can seek information over the Internet or call anyone over a public switched telephone network (“PSTN”) from any place inside the coverage area of the cellular wireless network.
In a typical cellular wireless system, an area is divided geographically into a number of cell cites, each defined by a radio frequency (“RF”) radiation pattern from a respective base transceiver station (“BTS”) antenna. The base station antennae in the cells are in turn coupled to a base station controller (“BSC”), which is then coupled to a telecommunications switch (e.g., a mobile switching center (“MSC”)) or a gateway (e.g., a packet data serving node (“PDSN”)) that provides connectivity with a transport network, such as the PSTN or the Internet.
When a wireless device is positioned in a cell, the wireless device and the base station can communicate with each other in various channels over the RF air interface. Communications from the base station to a wireless device are considered to be in a “forward” direction, so the air interface channels used to carry such communications are referred to as the “forward link” channels. Conversely, communications from a wireless device to the base station are considered to be in a “reverse” direction, so the air interface channels used to carry such communications are referred to as “reverse link” channels. These directional labels, however, are merely arbitrary, and other orientations might also be used.
With the continued growth in popularity of wireless communications, people are increasingly engaging in cellular wireless communications in place of traditional landline communications. This is of course most notable within buildings, such as homes and offices, where landline communications, such as traditional telephones and computer networks, were once the only method available. Use of wireless devices instead of fixed landline terminals conveniently allows for free movement within such buildings as well as into and out of the buildings.
Unfortunately, however, cellular wireless communications can suffer from varying levels of signal degradation as signals are carried over the air interface between the wireless devices and the base station. Most significantly, for instance, the strength of signals transmitted in the forward link direction from the base station to the wireless device can diminish substantially as the signals travel over increased distance to the wireless device. Further, obstructions such as buildings and foliage can attenuate or otherwise degrade signals passing over the air interface.
When a wireless device operates within a building, the problem can be even more acute, as the structure of the building can further diminish the signal. In a worst case scenario, forward link signals that ultimately arrive at a wireless device within a building may be too weak to be detected and/or used by the wireless device. As a result, service could be unavailable and wireless communications could be blocked or dropped. This is clearly a problem for cellular wireless carriers who are seeking to promote in-building use of their services.
One approach that can be used to overcome this difficulty is to increase the power transmitted by the base station. A disadvantage with this approach, however, is that the increased power can lead to increased interference in adjacent cells. This, in turn, can decrease the capacity of the wireless network. The power increase can also interfere with other wireless devices in use around the base station. The magnitude of the power increase proportionally affects the amount of interference produced by the base station, with a greater power increase causing a greater interference.
Also, this approach would only solve half the problem. Increasing the signal strength from the base station would allow a wireless device to receive the base station's signals in areas that highly attenuate that signal. It would not aid the base station in receiving signals from a wireless device. Cellular service is primarily a bi-directional mode of communication, in which connections are established and maintained through control signals that are sent in both directions between the base station and a wireless device. Therefore, in order to support bi-directional communication, an increase in the transmission power of the base station would require a corresponding increase in the transmission power of the wireless device.
Another approach to help increase wireless signal strength within a building is to provide a distributed antenna system in the building. In this approach, a hub is connected, via wired links, to one or more repeaters in the building. The wired link is typically a coaxial cable, a 10 Base-T cable or a fiber optical cable. The hub transmits the RF signals from the base station to the repeaters via the wired links. The repeaters, in turn, transmit the RF signals into the building, where they may be received by wireless devices. Similarly, the repeaters receive RF signals transmitted by the wireless devices and in turn transmit the RF signals to the hub via the wired links. The hub, in turn, transmits the RF to the base station. In this way, the wireless coverage area provided by the base station may be enhanced within the building.
A disadvantage to this approach, however, is that the repeaters remain active regardless of whether any wireless devices are in range of the repeaters. In addition to needlessly broadcasting signals that would not then be received by any wireless device, the repeaters would continue to consume power and other wireless network resources. Although the repeaters might be deactivated or placed in a standby mode, they might not then be readily available when a wireless device moves within range.
Therefore, there exists a need from an improved way of implementing in-building repeaters for a wireless network.